The enormous success of the Internet has led to constant development and deployment of new features and services that have increasingly placed its technical foundations under stress. This has given credence to the notion that re-architecting the current distribution of functions in an IP network would lead to significant benefits in network stability, simplification of network operations, and flexibility in introduction of new network protocols and services.
Traditional router architectures are becoming complex. Despite the end-to-end architecture design principle that aims at a simple core network, traditional router architectures have gotten increasingly complex today. As new features are being defined in requests for comments (RFCs), more and more control plane complexity is being added at the routers. These features include routing (e.g., BGP-based MPLS-VPNs), traffic engineering (e.g., OSPF-TE), security, and the like. In fact, the code complexity of an IP router now rivals that of a telephony switch. In contrast, the forwarding path implementation has progressively become easier with rapid advances in large-scale hardware integration (e.g., ASIC) and ready availability of off-the-shelf chips.
Traditional IP networks are constructed using routers that operate relatively autonomously. The potentially unmanageable complexity is present at many points all over the network. This has many undesirable consequences. First, the multiple points of control significantly increase operational complexity (e.g., misconfiguration). Second, in certain circumstances, uncoordinated actions of these autonomous routers can lead to sub-optimal performance (e.g., poor recovery time) at best and network instability in the worst case. Finally, the introduction of new features may require upgrades to a large number of routers, which is both complex and error-prone.
Many advanced network management tasks, such as routing policy enforcement and traffic engineering would benefit significantly from the availability of a network-wide view. For instance, several common BGP-induced network stability and operations problems would be solved by moving BGP from individual routers to a single entity with autonomous system (AS)-wide scope. Similarly, many management functions require a network-wide view, without which a network can exhibit oscillation and poor stability. However, network-wide control is difficult and cumbersome to achieve in today's network of autonomous and complex routers.
Traditional router architectures have integrated control and forwarding. The control processors implementing control plane functions are co-located with the line cards that implement forwarding functions and often share the same router backplane. The control processors provide control functions only to the co-located line cards, and vice-versa, leading to a scenario where the line cards cannot be managed when there is a failure of the co-located controller(s).
In the traditional router architectures, the underlying theme is the deep intertwining of control and forwarding functions in current routers. There is a need to deconstruct routers to keep most of the network entities as dumb as possible by reducing their function to support only a few canonical packet forwarding functions and migrate all control protocols and non-forwarding related state and control processing to a few smart network-based control entities with the primary function of network-wide control.